C++: Model operator new and operator new[].

cpp/ql/src/semmle/code/cpp/exprs/Expr.qll

@@ -2,6 +2,7 @@ import semmle.code.cpp.Element
 private import semmle.code.cpp.Enclosing
 private import semmle.code.cpp.internal.ResolveClass
 private import semmle.code.cpp.internal.AddressConstantExpression
+private import semmle.code.cpp.models.implementations.Allocation
 
 /**
  * A C/C++ expression.
@@ -804,8 +805,10 @@ class NewOrNewArrayExpr extends Expr, @any_new_expr {
    * call the constructor of `T` but will not allocate memory.
    */
   Expr getPlacementPointer() {
-    isStandardPlacementNewAllocator(this.getAllocator()) and
-    result = this.getAllocatorCall().getArgument(1)
+    result =
+      this
+          .getAllocatorCall()
+          .getArgument(this.getAllocator().(OperatorNewAllocationFunction).getPlacementArgument())
   }
 }
 
@@ -1194,12 +1197,6 @@ private predicate convparents(Expr child, int idx, Element parent) {
   )
 }
 
-private predicate isStandardPlacementNewAllocator(Function operatorNew) {
-  operatorNew.getName().matches("operator new%") and
-  operatorNew.getNumberOfParameters() = 2 and
-  operatorNew.getParameter(1).getType() instanceof VoidPointerType
-}
-
 // Pulled out for performance. See QL-796.
 private predicate hasNoConversions(Expr e) { not e.hasConversion() }
 

cpp/ql/src/semmle/code/cpp/models/implementations/Allocation.qll

@@ -215,6 +215,39 @@ class SizelessAllocationFunction extends AllocationFunction {
   }
 }
 
+/**
+ * An `operator new` or `operator new[]` function that may be associated with a `new` or
+ * `new[]` expression.  Note that `new` and `new[]` are not function calls, but these
+ * functions may also be called directly.
+ */
+class OperatorNewAllocationFunction extends AllocationFunction {
+  OperatorNewAllocationFunction() {
+    exists(string name |
+      hasGlobalOrStdName(name) and
+      (
+        // operator new(bytes, ...)
+        name = "operator new" or
+        // operator new[](bytes, ...)
+        name = "operator new[]"
+      )
+    )
+  }
+
+  override int getSizeArg() { result = 0 }
+
+  override predicate requiresDealloc() { not exists(getPlacementArgument()) }
+
+  /**
+   * Gets the position of the placement pointer if this is a placement
+   * `operator new` function.
+   */
+  int getPlacementArgument() {
+    getNumberOfParameters() = 2 and
+    getParameter(1).getType() instanceof VoidPointerType and
+    result = 1
+  }
+}
+
 /**
  * An allocation expression that is a function call, such as call to `malloc`.
  */